New Equine Test

Occipitoatlantoaxial Malformation (OAAM)

Description:

Occipitoatlantoaxial malformation (OAAM) is an autosomal recessive developmental skeletal defect which causes compression of the upper cervical cord. This malformation of
the occipital bone of the skull results in a neurologic disorder caused when the first two cervical vertebrae (the atlas and axis), fuse to the base of the skull. This structural change creates pressure on the upper portion of the cervical spinal cord, damaging the tissue.

The disease may progress with age from mild incoordination and weakness of the limbs to the inability to stand. Depending on the severity of the disorder affected foals may be
stillborn, show signs at birth or, in some cases, not show signs until a few weeks after birth.

Diagnosis of the malformed atlas and axis is generally confirmed with
radiographs. Affected foals are generally euthanized.

In order for a foal to be affected, it must be homozygous (have two copies) for the
mutated gene, inheriting a single copy from each parent. Horses that have one copy of the mutated gene are not affected but are considered carriers and, if bred, have a 50% chance of passing on the mutated copy to its offspring.